Metal pipe straightening method, straightening roller, and manufacturing device

ABSTRACT

A straightening method is presented where a concave roller, which has a roller caliber and in which the projection of the roll caliber forms an arc with respect to the cross section of a pipe. The projection arc radius can freely be changed by adjusting the angle between the roller axis and the axis line of the pipe. A plurality of concave rollers are arranged on the outer surface of the metal pipe in the circumferential direction, and rolling is applied on the outer diameter of the pipe while revolving these rollers about the pipe axis.

BACKGROUND OF THE INVENTION

The present invention is a technology which can provide a metal pipe with a high level of circularity and a high level of straightness at a low-cost because of high productivity, and relates to a metal pipe straightening method and straightening roller and manufacturing device which straightens a metal pipe using a plurality of concave rollers without causing the metal pipe to rotate on its axis, and for instance, can perform a continuous sizing process in the manufacturing process of electrically welded pipe for instance.

Conventionally, as shown in FIG. 1, the continuous welding process of metal pipe represented by electrically welded pipe is generally comprising the steps of a preliminary process 2 wherein coil material 1 is uncoiled and prepared in a looper, a roll forming process 3 performed by a break down roller, cluster roller, and fin pass roller, a welding process 4, followed by a sizing process 5, which is immediately prior to a final cutting process 7 where the metal pipe is cut to the desired length, and in the sizing process 5, the circularity and straightness of the pipe is corrected by a straightening roller 6.

As shown in FIG. 2, the sizing process uses a double roller 6 (FIG. 2A) where the center axes are arranged orthogonal to the axis line of the pipe in the same plane, a triple roller 8 (FIG. 2B) or a quadruple quadruple roller 9 (FIG. 2C), and in any of these combinations, these rollers cover nearly the whole circumference of the outer surface of a pipe 10 to form a grooved pass.

When straightening is performed in the sizing process of a pipe production line as shown in FIG. 1, the sizing is efficiently and continuously performed, which is an advantage, but there are also the following problems. First, a grooved roll with dimensions nearly identical to the desired outer dimension is necessary, so when the outer dimension of the manufactured pipe is to be changed, a changeover operation is necessary where the sizing roll is rearranged and the roll positions adjusted, so high productivity cannot be obtained particularly for small lot diversified production.

Next, the mechanism of the straightening method which uses this grooved pass roll is to press and deform the pipe in the circumferential direction, but pipe which is manufactured by normal roll forming has widely varying deformation history received in the different regions in the circumferential direction, and therefore obtaining a high level of circularity is extremely difficult because of the effects of elastic recovery and residual stress or the like.

Furthermore, warping of the manufactured pipe is straightened by arranging a plurality of roller stands in the longitudinal direction of the pipe, but this straightening effect is limited to only certain regions in the circumferential direction of the pipe, so obtaining a high level of straightness is difficult.

In order to obtain finished product with a higher level of circularity and straightness than the precision of the metal pipe obtained by the manufacturing process shown in FIG. 1, the cut product normally must be resized and straightened in specialized straightening equipment such as a straightener or a draw dice.

For instance, when a straightener is used as shown in FIG. 3, three sets of rollers are arranged, and while rotating, the metal pipe 10 is passed between a pair of concave rollers 11, 11 in each set, and thereby each region of the pipe is repeatedly bent in the cross-sectional plane and in the longitudinal direction, thus making the shape dimensions and the internal stress uniform, and greatly improving both the circularity and the straightness.

If specialized straightening apparatus and equipment is used, a higher level of circularity and straightness can be obtained, but an additional process separate from the pipe manufacturing line is required, so the process must be performed on each individual pipe after cutting, and therefore productivity is poor, and additional equipment and stockyard are required, so the pipe manufacturing costs are also increased.

SUMMARY OF THE INVENTION

Therefore, as apparatus for continuous straightening in the pipe manufacturing process, a so called planetary type straightening method and apparatus is disclosed in Japanese Patent Application Laid-open Nos. H2-41706, H5-220507, and H7-246403 wherein a plurality of convex rollers are arranged concentric to the outer surface of the metal pipe, and while revolving about the axis of the pipe, these roller groups apply pressure on the outer diameter of the pipe.

The target of the planetary type straightening apparatus is to greatly improve productivity by both including the straightening process into the pipe forming process, and at the same time, providing a straightening roller. In other words, the rollers arranged about the outer surface of the pipe in the planetary system are aligned at an angle to the axis of the pipe, and this angle can be adjusted, so the degree of freedom to expand and contract in the radial direction of the pipe is relatively large and the rollers can be used for a certain outer dimension range of product.

However, with the planetary type straightening apparatus, the convex roller cannot restrain the whole circumference of the pipe cross-section with almost no gaps as good the conventional grooved pass roller, and therefore it is extremely difficult to effectively press and deform the pipe in both directions. However, this type of technology disclosed in the aforementioned literature uses the same basic straightening mechanism to press on the circumferential direction of the pipe as the conventional method.

In actuality, as shown in FIG. 4A-C, when pressure is applied without restraining the whole circumference of the cross-section of the pipe 10, a plurality of convex rollers 12 are used, so the form and strength of the retention received by the cross-section of the pipe will vary along the axial direction of the pipe more than when the whole circumference of the pipe 10 is restrained and deformed. Furthermore, because rotation about the axis of the pipe by the rollers 12 proceeds at the same time as the metal pipe 10 proceeds, the way that each section of the pipe will deform is not fixed, so obtaining the desired circularity and straightness cannot be guaranteed.

In other words, from the aspect of commonizing rollers and productivity, the planetary type straightening apparatus has great advantages which other straightening apparatus do not have, but as described above, there are technical problems with the basic straightening mechanism of the pressing process in the circumferential direction of the pipe, so the advantages have not been sufficiently achieved to date.

An object of the present invention is to propose a metal pipe straightening method and straightening roller and metal pipe production apparatus which can be implemented continuously in the sizing process of the electrically welded pipe manufacturing process, and which can inexpensively provide metal pipe with a high level of circularity and a high level of straightness while maintaining high productivity and commonizing the rollers.

In order to perform continuous sizing in the pipe manufacturing process and to commonize rollers, the present inventors thought it was necessary to escape the thinking of conventional pressing processes, and implement a more accurate straightening mechanism, and as a result of various investigations, have focused on the fact that repeatedly bending the pipe was easy when considering the restraining form of the metal pipe in a conventional planetary type straightening apparatus.

As a result of diligent investigations concerning the roller caliber of the straightening roller, the present inventors have discovered that a continuous repetitive bend can be applied to all regions in the circumferential direction of the cross-section of the pipe utilizing revolution of the roller group if the roller caliber is such that the shortest distance from the roller surface to the pipe axis is a certain value in any cross-section in the axial direction of the pipe, and the present inventors have confirmed that an objective of the present invention can be achieved if a concave roller with this specific roller caliber is used, a straightening roller group is constructed of a plurality of these concave rollers arranged in the circumferential direction of the outer surface of the metal pipe, and pressure is applied to the pipe to straighten the outer circumference of the pipe while the roller group is revolving about the axis of the pipe.

In other words, the present invention is a method to straighten the outer circumference of a pipe by arranging a plurality of concave rollers in the circumferential direction of the outer surface of a metal pipe, and applying pressure to the pipe while revolving the roller group about the axis of the pipe, wherein the roller calibers of each of the rollers which contact the metal pipe has a structure where parts of the projection of the roller surfaces with respect to the cross-section of the pipe are on an identical circumference, and the radius of the projected circumference can be changed by determining the angle of inclination of the roller to the axis of the pipe and the position in the radial direction of the pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process explanatory diagram showing the continuous manufacturing process for metallic pipe;

FIG. 2A-C are explanatory diagrams showing the structure of various conventional groove pass rollers;

FIG. 3 is a perspective view explanatory diagram showing the structure of a conventional straightener;

FIG. 4A is a perspective view explanatory diagram showing the operating principle of a conventional planetary type straightening apparatus;

FIG. 4B is a schematic diagram showing the restraint condition of the pipe;

FIG. 4C is an explanatory diagram showing the roller pressed condition;

FIG. 5 is an explanatory diagram showing the relationship between the metal pipe and concave type straightening rollers according to the present invention, wherein A is the view from the top surface and B is the view in the axial direction of the pipe;

FIG. 6 is an explanatory diagram showing the relationship between the metal pipe and a straightening roller group of concave straightening rollers according to the present invention, wherein A is the case of a small diameter pipe and B is the case of a large diameter pipe;

FIG. 7 is a graph showing the relationship between the distance from the roller width center and the distance from the rotational axis of the roller for a preferred embodiment of the present invention; and

FIG. 8A-B are explanatory diagrams showing the eccentric relationship between the straightening roller group according to the present invention and the metal pipe.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have considered the characteristics of the restraining form of a metal pipe in a planetary type straightening apparatus, have focused on the fact that repeatedly bending a pipe is easy, and have conceived a structure which can introduce the same straightening mechanism as the aforementioned straightener. In other words, the ability to achieve this type of mechanism is directly related to the design of the roller caliber.

Only the fact that each region in the circumferential direction of the pipe is randomly bent and deformed by a standard convex roller caliber is as previously described, and the present inventors have discovered that a continuous repetitive bend can be applied to all regions in the circumferential direction of the cross-section of the pipe utilizing revolution of the roller group if the roller caliber is such that the shortest distance from the roller surface to the pipe axis is a certain value in any cross-section in the axial direction of the pipe.

As shown in FIG. 5, the straightening roller according to the present invention is concave rather than convex, and this roller form is required to meet the aforementioned conditions. In detail, as shown in FIG. 5A, the trail on the surface of the pipe by the roller 20 which is the shortest distance is shown by curved line A-B-O-C-D, but as shown in FIG. 5B when looking at the pipe 10 from the axial direction, the projection A′-B′-O′-C′-D′ forms an arc 21.

Therefore, as shown in FIG. 6, according to the present invention, if a straightening roller group 22 is constructed using three straightening rollers 20, and all of the rollers 20 are concentric and arranged at the same angle of inclination (α) to the axis of the metal pipe 10, a part of the projection of the surface of each roller 20 on the cross-section of the metal pipe 10 will be on the same circumference (Hereinafter this circumference is referred to as the projection circumference).

In other words, the straightening method according to the present invention is comprising the step of applying pressure to a pipe and straightening the outer circumference of the pipe while revolving about the axis of the pipe a correction roller group wherein a plurality of concave rollers having a roll caliber are arranged in the circumferential direction of the outer surface of the metal pipe wherein the roller caliber of the concave rollers which contact the metal pipe is structured such that part of the projection of the roller surfaces on the cross-section of the metal plate are all on the same circumference and the radius of the projection arc can be adjusted according to the position of the rollers in the radial direction of the pipe and the angle of inclination of the rollers to the axial line of the pipe.

With the present invention, the sum of the angles of the projections of the concave straightening rollers 20 will not necessarily be 360 degrees in the circumferential direction of the pipe 10, but the straightening roller group 22 is revolving, so while any arbitrary cross-section of the metal pipe 10 passes through the restraining region of the roller group 22, each region in the circumferential direction of the pipe 10 can be pressed at least one time in the radial direction.

Furthermore, as the relative speed of the revolution of the roller group 22 increases in regards to the flow speed of the metal pipe 10, the number of times that each region in the same direction of the pipe 10 is pressed by the rollers 20 will increase, so the target straightness can be achieved by increasing the number of repeated bending deformations which occur when the region is pressed. With the present invention, roller caliber designs which have the aforementioned characteristics which meet a specific product outer diameter are of course possible, but in actuality, one of the strongest characteristics of the present invention is that the outer diameter of various products can be met by changing the angle of inclination of the rollers which have the same roll caliber.

For example, as shown in FIG. 7, if the roller calibers which can form projection circumferences with a radius of 25 millimeters, 50 millimeters, and 75 millimeters are designed at different respective angles of inclination and compared, the geometrical difference can be seen to be extremely small within a certain range of roll width. Furthermore, with the present invention, there is no practical problem with using a roll caliber for any straightening roller as a common caliber by restricting the roller width such that the difference is a value clearly smaller than the required circularity tolerance.

Therefore, the straightening roller according to the present invention is comprising a concave roller caliber with a structure wherein a part of the projection of the roll surface with respect to the cross-section of the metal pipe is on the same circumference, and the radius of the projection arc can be adjusted according to the position of the roller in the radial direction of the pipe and the angle of inclination of the roller with respect to the axis of the pipe.

With the planetary type and straightening methods disclosed to date, roller communization was primarily performed by adjusting the position of the rollers in the radial direction of the pipe, and the inclination of the roller was primarily to generate a propulsive force component in the direction of progression of the metal pipe.

In contrast, with the present invention, the inclination of the straightening roller is proactively utilized to achieve roller commonization. Incidentally, when rollers are commonized, there is a restriction to the roller width which can actually be utilized, and there is a possibility that repetitive bending will not be performed a sufficient number of times on an area of the cross-section of the metal pipe particularly in the communized range for large diameter products.

However, with the present invention, this problem can be resolved by arranging a plurality of straightening roller groups in tandem in the progressive direction of the pipe. Furthermore, using a plurality of straightening roller groups of the present invention, not only improves the circularity, but is also very effective for improving the straightness.

In other words, the metal pipe straightening method arranges in the axial direction of the pipe a plurality of straightening roller groups wherein a plurality of concave rollers having the aforementioned roller caliber are arranged in the circumferential direction of the outer surface of the metal pipe, and each roller group applies pressure to the pipe while revolving about the axis of the pipe in order to straighten the metal pipe.

Normally, the geometric center of the arrangements of rollers which make a roller group matches the center of revolution, or in other words, the projection circumference center and the roller group center of revolution are the same, and if the center of revolution for each roller group is arranged on the same straight-line (pass line), the metal pipe will not be repeatedly bent and deformed in the longitudinal direction when passing through these roller groups. In Japanese Patent Application Laid-open No. H7-246403, a method is disclosed where the bending of the pipe can be controlled by setting the center of revolution of part of the roller groups away from the pass line. However, unlike the case of the aforementioned straightener shown in FIG. 3, the metal pipe 10 does not rotate, so with this method, bending can only be controlled in the designated direction which are the same as that of the conventional sizing process.

With the present invention, in order for repetitive bending to the performed in the longitudinal direction without rotating the metal pipe, the projection circumference of the roller group and the center of rotation must beset to be different. In this case, the projection circumference will eccentrically rotate with respect to the center of revolution, so the regions in the circumferential direction of the metal pipe which are restrained in the projection circumference will successively be bent and deformed in the longitudinal direction. There are two methods to provide that the center of revolution of at least one straightening roller group will eccentrically revolve with respect to the center of revolution of the other straightening roller groups in order to improve the straightness of the pipe. The first method is to eccentrically rotate the center of rotation of part of the roller groups with respect to the pass line. In this case, as shown in FIG. 8A, the axis 30 of the region of the metal pipe 10 which is restrained by a straightening roller group comprising 3 straightening rollers 20 is constructed to eccentrically rotate with respect to the roller group and to rotate about the pass line 31. Note, in the figure, the center of revolution and the geometrical center of the roller positions match the axis of the pipe 30, and the single point broken line shows the course of travel for the revolution of the straightening roller, and the broken line shows the course of travel for the center of revolution.

In the aforementioned straightening method, a plurality of groups of straightening rollers are arranged in the axial direction of the pipe, the axis pass line of the whole metal pipe which passes through the plurality of straightening roller groups has an eccentric relationship to the metal pipe axis in the position which is the geometrical center of the arrangement of the rollers which form any one of the straightening roller groups, and which is the center of revolution thereof, and bending deformation is created in the longitudinal direction of the metal pipe which passes through, to increase the straightness in the axial direction of the pipe. The second method is to set the geometrical center of the roller arrangement of a straightening roller group and the corresponding center of revolution to be different. In this case, as shown in FIG. 8B, the geometrical center of the roller arrangement and the overlaying axis of the pipe 30 will eccentrically rotate with respect to the pass line 31 even though the center of revolution of the straightening roll group does not differ from the pass line 31. Note, in the figure, the axis of the pipe 30 matches the geometrical center of the arrangement of the rollers, and the center of revolution of the straightening roller group matches the pass line 31, the single point broken line shows the course of travel for the straightening roller revolution, and the broken line shows the course of travel of the geometrical center of the roller arrangement. Furthermore, if there is a need to apply relatively stronger straightening effects on a specific region (for instance a welded region of a welded pipe) as opposed to other regions of the pipe 10, the center of revolution of the roller group can be shifted from the pass line toward this specific region, and additional bending and deformation will be applied only in this region.

The aforementioned straightening method arranges a plurality of straightening roller groups in the axial direction of the pipe, and the geometrical center of the arrangement of the rollers which form any of the straightening roller groups and the center of revolution of that roller group have an eccentric relationship, and therefore bending and deformation can occur in the longitudinal direction of the metal pipe which passes through, and the straightness in the longitudinal direction of the pipe can be increased.

When the aforementioned straightening method according to the present invention is applied to the sizing process of welded pipe as described in FIG. 1, the complicated operation of exchanging rollers will not be necessary and productivity can be dramatically improved. Furthermore, because a positive straightening mechanism is incorporated, a product with a higher level of circularity and straightness can be obtained as compared to conventional sizing processes.

Furthermore, the present invention can show a similar effect if the aforementioned straightening method is used in the resizing process in a pipe mill which continuously produces metal pipe from metal straps in a forming process which has a form roller, a form shoe, or both.

Using the straightening method of the present invention as shown in FIG. 5 and FIG. 6, straightening the circularity and straightness of various outer diameters of pipe was attempted in the sizing process for welded steel pipe. The commonization range of the straightening apparatus which uses straightening rollers with the characteristics shown in FIG. 5 was compared to the various inclination angles of a roller caliber which can form projection circumferences corresponding to the dimensions of various metal pipes with diameters from 25 mm to 75 mm and was expressed in FIG. 7 as the relationship between the distance from the roller width center and the distance from the roller rotational axis.

As shown in FIG. 7, the roller calibers which could form a projection arc with a radius of 12.5 millimeters, 25.0 millimeters, and 27.5 millimeters had different respective inclination angles α, or in other words, when an inclination angle of approximately 27.5° was used for a metal pipe with a diameter of 25 millimeters, and an inclination angle of approximately 32.5° was used for a metal pipe with a diameter of 75 millimeters, in the range where there was a roll width, there was clearly very little geometrical difference. In other words, if the roll width is restricted so that the geometrical difference is clearly smaller than the value of the circular tolerance required, there will be no problem using any roll caliber as a common roll caliber, and in actuality, the circularity and straightness can be increased in pipes with a wide range of outer diameters.

The present invention is a new straightening method wherein a plurality of concave rollers which have a specific shape of roller caliber are arranged in the circumferential direction of the outer surface of a metal pipe to form straightening roller groups which apply pressure on the pipe while revolving about the axis of the pipe in order to straighten the pipe, and if this straightening method is applied to the sizing process of welded pipe, the productivity can be dramatically improved and complicated roller changeover operations will not be necessary.

The present invention implements a sure straightening mechanism, so compared to conventional sizing processes, a product with a higher level of circularity and straightness can be obtained, the sizing process can be continuously performed in the pipe forming process, high productivity and roller communization can be achieved, and a metal pipe with a high level of circularity and high level of straightness can be provided inexpensively. 

1. A metal pipe straightening method comprising: revolving a straightening roller group about the axis of a metal pipe to apply pressure to the metal pipe to straighten the outer circumference of the metal pipe, wherein said straightening roller group includes: a plurality of concave rollers with a roller caliber to be arranged in the circumferential direction of the outer surface of the metal pipe, the roller caliber of the concave roller, which is made to contact the metal pipe, having a structure in which parts of the projection of the roller surfaces on the cross-section surface of the metal pipe are on the same circumference of the metal pipe, and the radius of the projection arc can be adjusted according to the angle of inclination of the roller with respect to the axial line of the pipe and the position in the radial direction of the pipe.
 2. A metal pipe straightening method comprising: revolving about the axis of a metal pipe a plurality of straightening roller groups arranged in a axial direction of the metal pipe to apply pressure to the metal pipe to straighten the outer circumference of the pipe wherein each of the straightening roller groups include: a plurality of concave rollers with a roller caliber, which are arranged in the circumferential direction of the outer surface of the metal pipe, the roller caliber of the concave roller, which contacts the metal pipe, having a structure in which parts of the projection of the roller surfaces on the cross-section surface of the metal pipe are on the same circumference of the metal pipe, and the radius of the projection arc can be adjusted according to the angle of inclination of the roller with respect to the axial line of the pipe and the position in the radial direction of the pipe.
 3. The metal pipe straightening method according to claim 2, wherein a pipe axial pass line of the whole metal pipe, which passes through the plurality of straightening roller groups, has an eccentric relationship to the axis of the metal pipe in the position which is the geometrical center of the arrangement of the rollers, which form any of the straightening roller groups and which are the center of revolution thereof, and deformation by bending occurs in the longitudinal direction of the metal pipe, which passes through the roller groups in order to increase the straightness of the pipe in the axial direction.
 4. The metal pipe straightening method according to claim 2, wherein the geometrical center of the arrangement of the rollers, which form any of the straightening roller groups, has an eccentric relationship with the center of revolution of that roller group, and deformation by bending occurs in the longitudinal direction of the metal pipe, which passes through the roller groups in order to increase the straightness of the pipe in the axial direction.
 5. A metal pipe straightening roller, which is used in the metal pipe straightening method according to claim 1, wherein the roller caliber of concave rollers contacting the metal pipe is constructed such that parts of the projection of the surfaces of the rollers on the cross-section surface of the metal pipe are on the same circumference of the metal pipe, and the radius of the projection arc can be adjusted according to the angle of inclination of the roller with respect to the axial line of the pipe and the position of the rollers in the radial direction of the pipe.
 6. A manufacturing apparatus for a metal pipe comprising: an apparatus which continuously produces a metal pipe from metal strapping in a forming process which uses a forming roller, forming shoe, or both, and an apparatus which straightens the metal pipe after production in a sizing process, wherein the metal pipe straightening method according to claim 1 is used in the sizing process.
 7. A manufacturing apparatus for a metal pipe comprising: an apparatus which continuously produces a metal pipe from metal strapping in a forming process which uses a forming roller, forming shoe, or both, and an apparatus which straightens the metal pipe after production in a sizing process, wherein the metal pipe straightening method according to claim 2 is used in the sizing process.
 8. A metal pipe straightening roller which is used in the metal pipe straightening method according to claim 2, wherein the roller caliber of concave rollers contacting the metal pipe is constructed such that parts of the projection of the surfaces of the rollers on the cross-section surface of the metal pipe are on the same circumference of the metal pipe, and the radius of the projection arc can be adjusted according to the angle of inclination of the roller with respect to the axial line of the pipe and the position of the rollers in the radial direction of the pipe. 